GNU make manual 翻译( 一百四十二)

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5.7 Recursive Use of `make'

===========================



Recursive use of `make' means using `make' as a command in a makefile.

This technique is useful when you want separate makefiles for various

subsystems that compose a larger system.  For example, suppose you have

a subdirectory `subdir' which has its own makefile, and you would like

the containing directory's makefile to run `make' on the subdirectory.

You can do it by writing this:



     subsystem:

             cd subdir && $(MAKE)



or, equivalently, this (*note Summary of Options: Options Summary.):



     subsystem:

             $(MAKE) -C subdir

   

   You can write recursive `make' commands just by copying this example,

but there are many things to know about how they work and why, and about

how the sub-`make' relates to the top-level `make'.  You may also find

it useful to declare targets that invoke recursive `make' commands as

`.PHONY' (for more discussion on when this is useful, see *note Phony

Targets::).



   For your convenience, when GNU `make' starts (after it has processed

any `-C' options) it sets the variable `CURDIR' to the pathname of the

current working directory.  This value is never touched by `make'

again: in particular note that if you include files from other

directories the value of `CURDIR' does not change.  The value has the

same precedence it would have if it were set in the makefile (by

default, an environment variable `CURDIR' will not override this

value).  Note that setting this variable has no impact on the operation

of `make' (it does not cause `make' to change its working directory,

for example).

5.7 make 的递归使用
===========================

递归是使用 make 意味着在 makefile中把make 当作命令使用。这个技术在你想要一个大系统的每个子系统都有一个单独的makefile时候有用。例如，设想你有一个子目录 subdir ，有自己的makefile， 并且你想要包含此makefile的目录上的makefile来运行，你可以这样写:

subsystem:

cd subdir && $(MAKE)

或者，等价地，这样写(*note Summary of Options: Options Summary.):

subsystem:
$(MAKE) -C subdir

你可以用拷贝这个例子的方式来写自己的递归make 命令，但是也有很多如它们如何工作和为何如此工作以及子make如何和顶级make关联的东西需要知道。你也可以发现，声明激活递归式make指令为.PHONY很有用(若要参考更多相关信息，参见 *note Phony Targets::)。

为了方便起见，当 GNU make 启动(当它处理了任何的 -C 选项)，它设置了变量 CURDIR 到当前工作目录。make 不会再改变其值：特别是请注意，如果你从其他目录包含了文件，CURDIR 的值是不会改变的。如果是设置在makefile，优先级别也是一样。

 (缺省地，环境变量 CURDIR 无法覆盖此值)

请注意设置这个值对make 的操作没有影响(它不会导致make 改变当前工作目录)。

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